The present invention relates generally to wireless voice/data transmission and, more particularly, to the use of modulated-reflector technology for long-range and/or short-range, full-duplex cell phone communications.
In xe2x80x9cDo Cell Phones Need Warningsxe2x80x9d by Cathy Booth et al., Time, Oct. 9, 2000, it is stated that cell phone levels of radiation must be below the Federal Communications Commission""s xe2x80x9cspecific absorption ratexe2x80x9d ceiling which is a measure of the energy in watts per kilogram that one gram of body tissue absorbs from a cell phone indicating that there is a possible danger of using a cell phone.
A bidirectional communications link generally requires both a power transmitter and a receiver at each end of the link. Modulated microwave backscatter systems suitable for communications over tens of kilometers have been developed. The primary advantage of such systems is that bidirectional and high-bandwidth operation can be achieved with a conventional microwave transmitter and receiver at one end of the link, and a modulated reflector and microwave receiver at the other end of the link, there being no microwave energy generated by this end of the link. Transmission of standard monochrome video data requires a communications channel bandwidth of 4 MHz. However by using state-of-the-art video-compression techniques, it is possible to convey one image of standard video per second over a 5 kHz channel. Information rate capacity of modulated reflector channels depends upon antenna sizes, transmit power levels, background noise levels, distance between the ends of the link, desired picture quality, and other engineering tradeoffs.
In U.S. Pat. No. 5,075,632 for xe2x80x9cInterrogation and Detection Systemxe2x80x9d which issued to Howard A. Baldwin et al. on Feb. 21, 1978, a telemetering apparatus is described which includes a carrier wave generator which generates at least a single frequency RF signal, a transponder for receiving that signal and for amplitude modulating it in accordance with information selected for transmission, an antenna on the transponder for reflecting the amplitude modulated signal, and a receiver which is preferably located at the generator for processing the signal to determine the information carried thereby. There need be no large power source at the location of the transponder since no carrier signal is generated. Two or more transponder antennas may be interconnected into an array so as to receive and reflect a larger amount of carrier power. The carrier from the interrogator (carrier wave generator) can be beamed selectively to one or more transponders. Additionally, it is possible to get response from one transponder to two or more interrogators without interference by using different carrier frequencies where the frequency difference is outside of the modulation signal pass band. Baldwin et al. states that the carrier frequency Information can also be sent to the transponder unit from the interrogator by appropriately modulating the carrier sent from the interrogator, which could be performed in such as manner as not to interfere with the modulation superimposed on the reflected carrier signal at the transponder, for example, by using sufficiently separated modulation frequencies or by using different forms of modulation. Baldwin et al. states further that radio frequency transmitting and receiving antennas are well known to those skilled in the art, but no description of antennas suitable for this purpose is provided therein.
In U.S. Pat. No. 4,360,810 for xe2x80x9cMultichannel Homodyne Receiverxe2x80x9d which issued to J. A. Landt on Nov. 23, 1982, a similar modulated backscatter radio frequency identification system to that of Baldwin et al., supra. Both of these communication systems are half duplex or time-division full duplex, in that the interrogator to transponder communications using amplitude modulation are achieved during a certain time period, while transponder to interrogator communications are performed during another period of time.
Full duplex modulated-reflector communications links have been proposed for short-range applications, such as inventory control and livestock monitoring. For example, U.S. Pat. No. 5,649,296 for xe2x80x9cFull-Duplex Modulated Backscatter Systemxe2x80x9d which issued to John Austin MacLellan et al. on Jul. 15, 1997, describes a full duplex apparatus that can electronically update shelf-price labeling for use in retail sales. In such a system, both the interrogator and the transponder (or tag as the term is used in the ""296 patent) can transmit continuously and during the same time period. The duplex communication system includes an interrogator which generates a first modulated signal by modulating a first information signal onto a radio carrier signal. This first modulated signal is transmitted to at least one remote tag of the system. The remote tag receives and processes the first modulated signal received at its antenna. A backscatter modulator uses a second information signal to modulate the reflection of the first modulated signal from the antenna, the reflected signal being a second modulated signal. The interrogator receives and demodulates the second modulated signal to obtain the second information signal. The antenna described in MacLellan et al. is a loop or patch antenna, and an inexpensive, short range, bidirectional digital radio communications channel is implemented. MacLellan et al. also teach the use of phase modulation of the carrier signal which would require a more complex radio receiver in the tag capable of detecting phase-modulated signals. This phase-modulated signal would be modulated and backscattered by the tag. Specific implementations of this embodiment could include binary-phase-shift keying in the downlink and frequency-shift keying in the uplink (the path which is reflected and modulated by a device), or binary-phase-shift keying in the downlink and amplitude modulation in the uplink.
A similar technology may be found in U.S. Pat. No. 5,873,025 for xe2x80x9cModulated Backscatter Wireless Communication System Having An Extended Rangexe2x80x9d which issued to James Gifford Evans et al. on Feb. 16, 1999. Evans et al. also discloses that the invention described is relevant to any radio system utilizing modulated backscatter in which the object is to extend the range of the uplink path.
Antennas for modulated reflectivity systems are designed for reflecting a portion of the energy from the interrogator. Cell phones, by contrast, use wire monopole antennas having small areas and, therefore, poor ability to reflect incident radiation. Moreover, the manner in which cell phones are utilized effectively prevents alignment of the antenna with an incoming carrier wave. In U.S. Pat. No. 6,034,639 for xe2x80x9cRetractable Antenna For Portable Communicatorxe2x80x9d which issued to Roger R. Rawlins et al. on Mar. 7, 2000, a retractable antenna which includes an elongated cylindrical conductor enclosed by an elongated conductive sleeve is described.
Other antenna designs for cell phones include U.S. Pat. No. 5,995,052 for xe2x80x9cFlip Open Antenna For A Communication Devicexe2x80x9d which issued to Robert A. Sadler et al. on Nov. 30, 1999, where a planar antenna and a ground plane at a chosen angle therewith set for optimal operation of the antenna for the frequency of the communication device is described. The conductive element also shields the antenna from the effects of the human body. U.S. Pat. No. 5,966,098 for xe2x80x9cAntenna System For An RF Data Communications Devicexe2x80x9d which issued to Yihong Qi et al. on Oct. 12, 1999 describes a dipole antenna system which includes a first arm extending in a first direction and a second arm extending in a second direction that is not in the same line as the first direction. An electromagnetic coupler provides coupling between each dipole arm to establish a desired resonant bandwidth. Neither of these antenna designs is suitable for a modulated-reflectivity communications system.
U.S. Pat. No. 5,903,826 for xe2x80x9cExtremely High Frequency Multipoint Fixed-Access Wireless Communications Systemxe2x80x9d which issued to Richard Joseph Nowak on May 11, 1999 describes a directional antenna system for allowing access from a subscriber location to a fixed-access wireless communications system having a plurality of base-space stations which include a plurality of angularly spaced directional antenna facets each capable of receiving discriminately for a plurality of frequency sets two RF signals having orthogonal polarization. The antenna provides an angular coverage of 360xc2x0, one facet being focused on the basestation. The purpose of this antenna design is to provide a directional antenna for high frequency (approximately 30 GHz) operation that permits the subscriber to receive the best signal from a basestation which is not necessarily the closest base-space station; however, the directional antenna must be able to discriminate between which base-space station it is receiving the signal from if the base-space stations are all transmitting at the same frequency. The antenna is deployed in a cellular environment, and the performances of the signals received by the antenna facets are prioritized with the best performing facet being selected as the default facet. This manner of operation contemplates an antenna having a fixed, permanent spatial orientation. For bidirectional systems, the ""826 patent teaches that each antenna facet may have a single component which functions both to receive and transmit, or may have separate receive and transmit components. Nowak also teaches a single antenna facet which is rotatable to a point in various directions. The resting point of the rotatable facet would be determined by the radio controller, and one of a finite number of spaced angular positions would be chosen, each position assuming the roll previously filled by one facet in the multi-facet array.
Accordingly, it is an object of the present invention to provide a long-range cell phone communications system which does not emit significant radiation in order to respond to a received signal.
Additional objects, advantages and novel features of the invention will be set forth, in part, in the description that follows, and, in part, will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects of the present invention, and in accordance with its purposes, as embodied and broadly described herein, the radio communications system hereof includes: (1) a stationary system including: (i) means for generating an airborne carrier frequency; (ii) means for generating an airborne radio communication; and (iii) means for receiving and demodulating a modulated, reflected airborne carrier frequency; and (2) a mobile unit including: (a) data input means capable of generating electrical signals; (b) a passive transponder which includes: (i) an antenna having gain in a plurality of directions for receiving the modulated carrier frequency; (ii) an impedance switch in electrical connection with the antenna for varying the impedance thereof; and (iii) means for receiving the electrical signals from the data input means and for varying the impedance of the impedance switch in response thereto, thereby modulating the carrier frequency by varying the reflectivity of the antenna to the carrier frequency; (c) a radio receiver for receiving the airborne radio communication from the means for generating an airborne radio communication and generating electrical signals therefrom; and (d) data output means in electrical connection with the radio receiver for receiving the electrical signals generated thereby and generating an observable signal therefrom; whereby two-way radio communication is established between the stationary unit and the mobile unit.
It is preferred that the data input means includes a microphone.
Preferably, the data output means includes a speaker.
Benefits and advantages of the present invention include a handheld cellular phone unit that: (1) operates with little power consumption, thereby permitting lengthy airtime and reduced battery weight; (2) operates with no active RF radiation emitted from the cell phone antennas, thereby reducing radiation exposure to users; (3) operates over commercially viable long distances; (4) reduces hazardous waste generation due to smaller battery requirements; and (5) reduces spark generation potential for use in explosive environments.